The present patent application relates to an airless sprayer and in particular to an airless sprayer having a tungsten steel plunger with a nitride-hardened cylinder and/or piston and a process of manufacturing the same.
Airless sprayers are known in the art, for example, the Black and Decker Models Stain, Plus, and Deluxe. These sprayers are able to spray paint without the need for compressed air. They generally operate on the principle of high-speed oscillation of a steel piston within a steel cylinder, the oscillation of the piston in turn being produced by an electric motor. In order for the sprayer to work, there must be a very small clearance, on the order of 0.0002 to 0.0003 inches, between the piston and the cylinder. With this small clearance, there is no need for a seal because the liquid being sprayed creates a seal.
However, certain paints such as acrylic latex, contain silica, a very abrasive material. As this paint is being sprayed, the silica wears down the cylinder. When the clearance between the piston and cylinder reaches approximately 0.002 inches, the sprayer will cease working. This typically occurs after spraying approximately 25 gallons of acrylic latex paint. At this point, the cylinder must be replaced.
The present invention involves treating the cylinder with a nitride process that greatly hardens the cylinder. Applicant has found that this hardening approximately doubles or triples the life the cylinder.
Nitriding is a process that is known for hardening various metals such as cast iron, steel, stainless steel, some nickel-based alloys, and titanium. A typical process is the Ultraglow® process from Advanced Heat Treat Corp., 2825 Midport Blvd., Waterloo, IA 50703. This technology is used in industry to improve material properties and extend tool life. Some improvements include: reduced coefficient of friction, improved wear resistance, and increased fatigue life. These improvements can be achieved without making any changes to the core properties, resulting in comparatively high part ductility and impact strength. Nonessential subject matter indicating the state of the art is hereby incorporated by reference (“Design Considerations for Iron Nitriding” published by Advanced Heat Treat Corp.). Other typical processes that could be used are the Tougbnite Gas Soft Nitriding Process from Hightemp Furnaces, Limited, IC, 2nd Phase, Peenya Industrial Area, P.O. Box No. 5809, Bangalore—560 058 India; and the gas soft nitriding process from Trutec Industries.
The characteristics of plasma nitriding are established through the type and thickness of the compound zone, the surface hardness, and the nitriding-hardness depth (diffusion zone thickness). These qualities are contingent upon alloy content, microstructure condition, tensile strength, and the hardness of the material before the plasma nitriding treatment.
Specifications developed by Advanced Heat Treat Corp. (AHT) determine the process parameters to be used, depending on the type of metal and the desired case depth of the finished product. These parameters are proprietary to AHT and do not form part of this patent application. However, the structure of the nitrided cylinder does form part of the present application, as well as the method of manufacture using the nitriding process.